Training balls for varying ball speed, methods of use, and systems

ABSTRACT

Methods and apparatus provide for at least one ball, comprising: a hard shell of a predetermined size defining an internal volume and including a plurality of apertures therethrough; and a foam core disposed within the internal volume.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 60/917,805, filed May 14, 2007, the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed to balls, methods of use, and systems thereof that employ a foam core disposed within a hard shell of a ball for teaching a person to hit balls at various speeds.

BACKGROUND OF THE INVENTION

Athletic balls, such as baseballs, softballs, or the like, are typically manufactured in standard sizes and have standard ball densities for maintaining certain aerodynamic characteristics depending on sport requirements. By way of example, when learning to hit a baseball, children traditionally first learn to hit a ball at a relatively constant speed and at a relatively constant position. Indeed the coach or parent will usually release successive pitches at the same velocity (slow) and to a particular position (dead center) over the plate until the batter learns how to track the pitch and strike the ball consistently.

Once the child has learned to track and hit the ball consistently when pitched at the same speed/position, the next step may be to learn how to hit the ball at various locations over the plate. This training should begin as the child's age permits if it is to be effective in improving the child's athletic performance. Indeed, for a player to become a well rounded and resilient batter, the player must learn to anticipate and hit the ball at the various positions over the plate. Thus, the coach will begin pitching successive balls to different plate positions to test or strike out the batter. Up until the age of about 10 years old, the coach will still pitch at a constant speed (no intentional change ups) even though he or she may intentionally change the plate position of the ball with successive pitches.

Typically, when a batter is around ten to eleven years old, the next step during the batting training process is for the batter to anticipate and learn to hit balls at various speeds and different locations. To help the batter learn to hit a ball at different speeds, a coach, pitcher, or the like, will alter his or her pitching motion with successive pitches in order to change the speed of the ball during practice. In order for a batter to maintain striking consistency as the pitchers to which he/she faces become more skilled, the batter must learn to keep his eye on the ball, track and strike balls travelling at different speeds. Batters must learn to hit a myriad of pitches, such as, but not limited to, fast balls, curve balls, knuckle balls, change ups, or the like. As these different types of pitches cannot be anticipated by viewing the way the pitcher grasps the ball prior to the pitch, the young batter must keep close watch on the ball and develop the ability to track the ball all the way to the plate irrespective of how fast the ball is travelling. Prior to developing this skill, a young batter will typically lose sight of the ball within about the last fifteen feet before the plate.

The problem with this learning approach is that typical coaches (or aspiring young pitchers) are not skilled enough to properly alter the speed of travel of the ball without altering their pitching motion in a visible way. Indeed, the pitching motion of a well thrown change-up should not be detectable from the throwing motion itself. Indeed, it is relatively easier for a coach or young player to pitch at a consistent release velocity (given a consistent ball size and density), than to pitch a change-up. Often, the coach must alter the pitching motion in some visible way (e.g., significantly slow down the motion) to achieve a slowly travelling ball. This gives the batter notice that a differing ball speed will be coming and does not test the batter's ball tracking ability. Even when a ball pitching machine is employed during practice, the machine is set to a particular speed and therefore releases the balls at a constant velocity. If the coach wishes to change the pitching speed, a clearly visible action must be taken at the mound, thereby giving the batter advanced notice that a change in pitch is coming. Consequently, young batters are subject to unintended variations in ball speed, and advanced notice of ball speed. Therefore, the traditional learning process is problematic because advances in the child's athletic ability are either unnecessarily delayed, or are arrested altogether.

One or more of the characteristics and problems discussed above with respect to teaching a player to hit a baseball may be applied to other areas of sport, such as softball, tennis, golf, ping pong, etc.

Therefore, there is a need in the art for new methods and apparatus for teaching a person to hit balls at various speeds.

SUMMARY OF THE INVENTION

One or more embodiments of the present invention provide a ball, method of use, and system that allow a person to learn how to hit similarly looking balls at various ball specific speeds when the balls are propelled towards the person in the same or similar way.

In accordance with at least one aspect of the present invention, a ball includes: a hard shell of a predetermined size defining an internal volume and including a plurality of apertures therethrough; and a foam core disposed within the internal volume.

A diameter of the foam core may be less than a diameter of the internal volume such that a layer of air is located between an outside surface of the foam core and an inside surface of the hard shell. Alternatively, the foam core may substantially fill the internal volume. When employing an air layer, at least one spacer may be disposed between the outside surface of the foam core and the inside surface of the hard shell, and adapted to position the foam core within the internal volume. The one or more spacers may be adapted to connect the outside surface of the foam core to the inside surface of the hard shell. For example, the at least one spacer may be formed of the core material, and/or the at least one spacer may be integrally formed with the foam core. A size and shape of the at least one spacer is operable to accommodate different distances from the inside surface of the hard shell to the outside surface of the foam core, such that the diameter of the foam core may be increased or decreased relative to the diameter of the hard shell.

At least one of a porosity and a composition of the foam core are preferably predetermined for a desired density.

In one or more embodiments, the foam core includes an inner portion having a first density and an outer portion having a second density surrounding the inner portion. The first density may be substantially higher than the second density. Alternatively or additionally, the inner portion may be formed from a material other than foam. Still further, the outer portion is preferably formed of foam irrespective of the inner portion.

The density is preferably such that it affects at least one aerodynamic characteristic of the ball, such as the speed that the ball travels through air when released at a predetermined velocity. When the structure of the ball is correctly established, the density may be linearly related to the speed. When an air layer is employed, the density of the foam core may be varied (from ball to ball) or may be fixed, however, the volume of the layer of air may be inversely related to the speed at which the ball travels when released at the predetermined velocity.

In accordance with one or more further aspects of the present invention, a method for teaching a person to hit a ball may include: providing a plurality of balls, each ball comprising: (i) a hard shell defining an internal volume and including a plurality of apertures therethrough, and (ii) a foam core disposed within the internal volume; and propelling the balls toward the person by releasing them, in turn, at a substantially constant velocity.

The construction of one or more of the balls may be as discussed above such that at least two of the balls travel through air at different speeds despite being released at the substantially constant velocity. Preferably the at least two balls travel through the air at speeds differing by at least about 10%, or least about 10% to about 20%. This simulates different pitches.

In accordance with one or more further aspects of the present invention, a system includes: a plurality of balls, each ball comprising: (i) a hard shell defining an internal volume and including a plurality of apertures therethrough; and (ii) a foam core disposed within the internal volume, wherein the foam core of at least one of the plurality of balls is adapted to cause such ball to travel through air at a substantially different speed as compared to at least one other of the plurality of balls despite the balls being released at the substantially constant velocity.

The advantages of this invention are best understood after reading the detailed description. Nonetheless, some of the advantages are aforementioned above.

Other aspects, features, advantages, etc. will become apparent to one skilled in the art when the description of the invention herein is taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purposes of illustrating the various aspects of the invention, wherein like numerals indicate like elements, there are shown in the drawings forms that may be employed, it being understood, however, that the invention is not limited by or to the precise arrangements and instrumentalities shown, but rather only by the claims.

FIG. 1 is a perspective view of an embodiment of a ball including a hard shell with apertures and containing a foam core in accordance with at least one aspect of the present invention.

FIG. 2 is a partially sectioned perspective view of an embodiment of a ball including a hard shell with apertures and containing a foam core with protrusions and an air layer between the foam core and hard shell in accordance with at least one aspect of the present invention.

FIG. 3 is a partially sectioned perspective view of an embodiment of a ball including a hard shell with apertures and containing a foam core with protrusions and an air layer between the foam core and hard shell in accordance with at least one aspect of the present invention.

FIG. 4 is a partially sectioned perspective view of an embodiment of a ball including a hard shell with apertures and containing a foam core having portions of differing density in accordance with at least one aspect of the present invention.

FIG. 5 is a schematic view of an embodiment of a ball system employing a plurality of similarly looking balls with different foam core densities in accordance with at least one aspect of the present invention.

FIG. 6 is a flowchart of an embodiment of a method of use of a ball in accordance with at least one aspect of the present invention.

FIG. 7 is a schematic view of an embodiment of a ball system employing a plurality of balls with different sizes in accordance with at least one aspect of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

In the following description, for purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one having ordinary skill in the art that the invention may be practiced without these specific details. In some instances, well-known features may be omitted or simplified in this description so as not to obscure the present invention. Furthermore, reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

For the purposes of describing various aspects of the present invention, reference may be made to a specific application of the present invention in connection with teaching a person how to hit a ball at different ball speeds. Indeed, embodiments of the invention have specific utility in the sports context where the sport requires the player to adjust his or her timing in response to changes in ball speed. Examples of such sports include baseball, softball, tennis, polo, rugby, football, ping pong, golf, volley ball, racquet ball, hand ball, etc. It will be appreciated by those skilled in the art, however, that the various embodiments of the balls, methods of use, and systems thereof described and claimed herein may have application to many other sports and/or other fields of endeavor. In the case of baseball and/or softball, the embodiments of the present invention have applicability for use in training sessions, such as, but not limited to, batting practice, scrimmages, games, or the like.

FIG. 1 is a schematic view of a ball 10 in accordance with at least one aspect of the present invention. The ball 10 may be for training a baseball or softball player (and may be referred to as such) or any of the aforementioned other applications. For example, in the context of baseball or softball practice, the ball 10 (or a plurality of such balls) may be used to teach a person to hit the ball at different speeds and locations using a bat. The ball 10 includes at least a hard shell 20 defining an internal volume, where the shell 20 includes a plurality of apertures 30 therethrough. The ball 10 also includes a foam core 40 disposed within the internal volume of the hard shell 20.

The hard shell 20 may have a size corresponding to a baseball, softball, tennis polo, rugby, football, ping pong, golf, volley ball, racquet ball, hand ball, etc. Those skilled in the art will recognize that the material of the shell 20 may be plastic, rubber, leather, combinations thereof, or other materials, although plastic is preferred. Although the hardness of the shell 20 can vary, a hardness along the lines of a standard wiffle-ball is preferred. The hard shell 20 can have a thickness of about 1/16 of an inch to ¼ of an inch, or greater. In a preferred embodiment, the hard shell 20 is about ⅛ of an inch thick.

The plurality of apertures 30 in hard shell 20 of a ball 10 can vary in size. In at least one embodiment, the apertures 30 are identical among a plurality of balls 10, irrespective of the desired aerodynamic characteristics. In a preferred embodiment, any change in size between apertures 30 of a ball 10 is designed to avoid detection by a batter so that the batter cannot judge the ball aerodynamics, e.g., ball speed, based on differences in the relative sizes of the apertures 30, particularly from ball-to-ball. Similarly, in order to avoid detection by the batter, in accordance with at least one embodiment, the hard shell 20 of the balls 10 has an equal or similar predetermined size, such that any deviation in the predetermined size is not detectable by the batter.

One or more of the hard shell 20, the apertures 30, and/or the foam core 40 may be designed to vary aerodynamic characteristics of the ball 10, such as, ball speed, air resistance, trajectory, rotational tendency, etc., for developing batting skills of a baseball or softball player.

By way of example, the foam core 40 is preferably adapted to cause the ball 10 to travel through air at a predetermined speed when released at a substantially constant velocity. For example, the foam core 40 of the ball 10 may be adapted to have a predetermined material composition and porosity in order to establish a desired density. The density of the foam core 40 may be linearly related to the speed at which the ball 10 will travel through the air when released at a substantially constant velocity. While not being limited to a particular theory of operation, this relationship may be expressed as follows:

Speed(d)=K+m(d),

where K is a constant of proportionality, m is a factor relating density to the speed at which the ball 10 will travel through the air when released at a substantially constant velocity, and d is the density of the foam core 40.

For a higher density, the foam core 40 is designed to have a lower porosity. Conversely, for a lower density, the foam core 40 is designed to have a higher porosity. Indeed, the porosity of the foam core 40 is inversely related to the density thereof, and thus an overall density of the ball 10.

In the embodiment illustrated in FIG. 1, the foam core 40 substantially fills the internal volume of the hard shell 20. Thus, in order to establish a desired aerodynamic characteristic of the ball 10, such as the speed at which the ball 10 will travel through the air when released at a substantially constant velocity, the density of the foam core 40 is adjusted, e.g., through foam material selection (porosity, composition, etc.) to achieve the desired characteristic. The density of the foam core 40 may need adjustment based on the size of the hard shell 20, the material properties of the hard shell 20, the size, frequency, and location of the apertures 30, etc.

In accordance with at least one embodiment of the present invention as shown in FIG. 2, a diameter of the foam core 40 may be less than a diameter of the internal volume of the hard shell 20 such that a layer of air 60 is located between an outside surface of the foam core 40 and an inside surface of the hard shell 20. The ball 20 may further include at least one protrusion 50 (or spacer) disposed between the outside surface of the foam core 40 and the inside surface of the hard shell 20. In a specific implementation, the spacers 50 are adapted to connect the outside surface of the foam core 40 to the inside surface of the hard shell 20. The spacers 50 operate to locate the foam core 40 within the volume of the hard shell 20 to establish the layer of air 60. Those skilled in the art will appreciate one or more relationships between the size, shape, and/or location of the spacers 50 and the size and shape of the layer 60. For example, as the diameter of the foam core 40 decreases, the spacers 50 may increase in length (and/or other characteristics, such as shape, location and/or number) in order to establish a layer of air 60 that increases in thickness and volume. For example, as shown through comparison of the ball 10 of FIG. 2 and the ball 10 of FIG. 3, one can see that the diameter of the foam core 40 decreases, the size (e.g., length and width) of the spacers 50 increases, and the thickness and volume of the layer of air increases (see difference between the layer of air 60 of FIG. 2 versus the layer of air 65 of FIG. 3).

The characteristics of the layer of air 60, 65 (even assuming a constant density of the foam core 40) can affect the aerodynamic properties of the ball 10. For example, as the layer of air 60, 65 increases in thickness and volume, while maintaining the density of foam core 40 and the velocity at which the ball 10 is released, the speed at which the ball 10 will travel through air will decrease. This is due to the fact that the air resistance of the ball 10 will increase as the layer of air 60, 65 increases in volume. Conversely, as the thickness of the layer of air decreases (e.g., as is the case from layer 65 to layer 60), while maintaining the density of foam core 40 and the velocity at which the ball 10 is released, the speed at which the ball 10 will travel through the air will increase. Those skilled in the art will appreciate that as the size (e.g., especially the length) of the spacers 50 increase or decrease and the diameter of the foam core 40 decreases or increases, the density of the foam core 40 may be adjusted to achieve the same aerodynamic properties, such as speed of travel as a function of release velocity. As shown in FIG. 2, the ball 10 has a foam core 45 with a different density than the density of foam core 40 of ball 10 as shown in FIG. 1.

In another embodiment, a layer of air may be defined without any spacers 50 disposed between the foam core 40 and the hard shell 20 so long as the foam core 40 has a diameter that is less than a diameter of the hard shell 20. In such a case, the foam core 40 is permitted to move within the internal volume of the hard shell 20.

The spacers/protrusions 50 may be formed from a separate material (such as foam or other suitable material) that is disposed between the foam core 40 and the hard shell 20. Alternatively, the spacers 50 may be integrally formed with the foam core 40 of the same foam material. The spacers/protrusions 50 have a shape, such as, but not limited to, suspension spikes, radiating spikes, raised support surfaces, or the like. In yet another embodiment, one or more of the spacers/protrusions 50 may be made of a foam material that has a different density than a portion of, or the entire, foam core 40. The spacers/protrusions 50 may be hard or soft, such that they may flexibly or elastically vary the distance or distances between the outside surface of foam core 40 and the inside surface of hard shell 20.

The foam core 40 may be formed from any number of specific materials, such as nylon, acetal, teflon, polycarbonate, acrylic, polyurethane blend, polyethylene, polystyrene, urethane, polyester, polypropylene, neoprene, rubber cork, black nitrile, silicone, plastic, hyplon, fluorocarbons, ethylene propylene diene monomer rubber, elastomer, ceramic, acetate, urea, polymethylpentene, acrylonitrile butadiene styrene, polyetheretherketone, polyvinyl chloride, or the like. The foam core density may be between about 1 to 300 kg/m³, 1 to 100 kg/m³, 1 to 10 kg/m³, 1 to 5 kg/m³, 5 to 10 kg/m³, 10 to 30 kg/m³, and 15 to 20 kg/m³.

The foam core 40 may be custom ordered or pre-manufactured by foam manufacturers, such as Precision Plastic Ball Company of Franklin Park, Ill.; Lendell Mfg., Inc. of Saint Charles, Mi; Foamex of Eddystone, Pa.; RHH Foam Systems, Inc. of New Berlin, Wis.; Quality Foam of Lake Elsinore, Calif.; Wisconsin Foam of Madison, Wis.; UFP Technologies, Inc. of Georgetown, Mass.; and Gardico of Seattle, Wash.

As shown in FIG. 4, the foam core 40 may further include an inside portion 70 and an outside portion 40 surrounding the inside portion 70. The inside portion 70 of the foam core 40 has a first density and the outside portion 40 has a second density. The first density and second densities may be different, with a preferred configuration being when the first density is substantially higher than the second density. The inside portion 70 may or may not be foam, the preferred material not being foam. The outer portion 40 is preferably formed of foam.

As discussed above, in order for a batter to improve his batting skill, the batter must test and improve his ability to track approaching balls 10 travelling at different speeds. In this regard, reference is now made to FIGS. 5-6. FIG. 5 illustrates a plurality of balls 10 a, 10 b, 10 c, 10 d, 10 e, 10 f, where each ball 10 includes the aforementioned configuration: (i) a hard shell defining an internal volume and including a plurality of apertures therethrough; and (ii) a foam core disposed within the internal volume. The foam core of at least one of the plurality of balls 10 is adapted to cause such ball to travel through air at a substantially different speed as compared to at least one other of the plurality of balls despite the balls being released at a substantially constant velocity.

In this regard, any of the aforementioned variations in foam density, foam core diameter, spacer size and/or position, etc. may be employed to achieve the desired differing aerodynamic characteristics of the plurality of balls 10 a, 10 b, 10 c, 10 d, 10 e, 10 f. In a preferred system, some of the balls 10 are configured to travel through the air at speeds differing by at least about 5% to about 20%, such as 16 mph, 20 mph, 24 mph, etc.

The plurality of the balls 10 all preferably have substantially equal size (e.g., a deviation of the ball size is no greater than about 5%, 2%, or 1%) and are otherwise of similar visual appearance, e.g., with respect to the location of apertures 30, color, etc.

Now referring to FIG. 6, in accordance with another aspect of the present invention, a method is disclosed for teaching a person to hit the plurality of balls 10, wherein at least one of the balls travels at a substantially different speed even though each ball may be released at the same velocity. As aforementioned, it is effective for a person to learn to hit the ball 10 through tracking the ball 10 itself and not through guessing what the speed may be based on a propelling motion. At action 100 a plurality of balls 10 are provided as discussed above. At action 102 the balls 10 are pitched toward the person by releasing them, in turn, at a substantially constant velocity. This may be carried out manually (e.g., by a coach) or using an automated machine. At action 104, the different balls 10 travel toward the person, in turn, at different respective speeds. At action 106, the person tracks the different balls 10, as discussed above, at the different respective speeds. When tracking the balls 10, the person may swing at or let the ball pass depending on the person's comfort with the aerodynamics of the propelled balls 10.

Within the group of balls 10, some have different aerodynamic characteristics (as discussed with respect to FIG. 5). Thus, as the balls 10 are propelled toward the player in the same way, technique or motion, each of the propelled balls 10 is released with the same velocity toward the person to preserve the conditions of the predetermined propelling motion. At least some of the balls 10 will travel towards the person at different speeds despite being propelled in the predetermined motion and at the same release velocity. Thus, the speed of at least some of the balls 10 will deviate from one another by more than about five percent. When a speed changes by more than about five percent, the batter is likely to notice the difference in speed and improve his or her skill at tracking the ball. The amount of time between ball propulsions can be fixed, or a person can indicate that he is ready for the next ball 10. This process is repeated in order to improve the person's tracking and hitting ability.

As shown in FIG. 7, balls 10 g, 10 h, 10 i, 10 j may have differing sized hard shells 20. Because different sized balls 10 exhibit different batting characteristics, the person batting must focus on delaying his swing until the person can accurately judge the speed of the ball 10. Under these types of situations, ball speeds can deviate more than about five percent, about ten percent to twenty percent, about ten percent to fifteen percent, and more than about fifteen percent between different balls 10 in the plurality. Ball speeds can vary because aerodynamic factors vary between balls 10 at a difference of more than about five percent, about ten percent to about twenty percent, about ten percent to about fifteen percent, about fifty percent to about one hundred percent, and about one hundred percent to about four hundred percent.

It is noted that although specific examples have been described in the context of baseball batting training, those skilled in the art may readily adapt the methods and apparatus herein to assist in training players in other sports, such as softball, tennis, polo, rugby, football, ping pong, golf, volley ball, racquet ball, hand ball, etc.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. 

1. A ball, comprising: a hard shell of a predetermined size defining an internal volume and including a plurality of apertures therethrough; and a foam core disposed within the internal volume.
 2. The ball of claim 1, wherein a diameter of the foam core is less than a diameter of the internal volume such that a layer of air is located between an outside surface of the foam core and an inside surface of the hard shell.
 3. The ball of claim 2, wherein the foam core fills the internal volume.
 4. The ball of claim 2, further comprising at least one spacer disposed between the outside surface of the foam core and the inside surface of the hard shell, and adapted to position the foam core within the internal volume.
 5. The ball of claim 4, wherein the at least one spacer is adapted to connect the outside surface of the foam core to the inside surface of the hard shell.
 6. The ball of claim 5, wherein at least one of: the at least one spacer is formed of the core material, and the at least one spacer is integrally formed with the foam core.
 7. The ball of claim 4, wherein a size and shape of the at least one spacer is operable to accommodate different distances from the inside surface of the hard shell to the outside surface of the foam core, such that the diameter of the foam core may be increased or decreased relative to the diameter of the hard shell.
 8. The ball of claim 1, wherein a composition of the foam core is taken from the group consisting of: nylon, acetal, teflon, polycarbonate, acrylic, polyurethane blend, polyethylene, polystyrene, urethane, polyester, polypropylene, neoprene, rubber cork, black nitrile, silicone, plastic, hyplon, fluorocarbons, ethylene propylene diene monomer rubber, elastomer, ceramic, acetate, urea, polymethylpentene, acrylonitrile butadiene styrene, polyetheretherketone, and polyvinyl chloride.
 9. The ball of claim 1, wherein at least one of a porosity and a composition of the foam core are predetermined for a desired density.
 10. The ball of claim 9, wherein the foam core includes an inner portion having a first density and an outer portion having a second density surrounding the inner portion.
 11. The ball of claim 10, wherein at least one of: the first density is substantially higher than the second density; the inner portion is not formed of foam; and the outer portion is formed of foam.
 12. The ball of claim 9, wherein the density affects at least one aerodynamic characteristic of the ball.
 13. The ball of claim 9, wherein the density of the foam core is related to a speed at which the ball travels through air when released at a predetermined velocity.
 14. The ball of claim 12, wherein the density is linearly related to the speed.
 15. The ball of claim 9, wherein the density of the foam core is at least one of: 1 to 300 kg/m³, 1 to 100 kg/m³, 1 to 10 kg/m³, 1 to 5 kg/m³, 5 to 10 kg/m³, 10 to 30 kg/m³, and 15 to 20 kg/m³.
 16. The ball of claim 9, wherein a diameter of the foam core is less than a diameter of the internal volume such that a layer of air is located between an outside surface of the foam core and an inside surface of the hard shell; and a volume of the layer of air is inversely related to a speed at which the ball travels through air when released at a predetermined velocity.
 17. The ball of claim 1, wherein the size of the hard shell is a size of one of: a ping pong ball, a golf ball, a baseball, a softball, a tennis ball, a polo ball, a rugby ball, a football, a soccer ball, a volley ball, a racquet ball, and a hand ball.
 18. A method for teaching a person to hit a ball, comprising: providing a plurality of balls, each ball comprising: (i) a hard shell defining an internal volume and including a plurality of apertures therethrough, and (ii) a foam core disposed within the internal volume; and propelling the balls toward the person by releasing them, in turn, at a substantially constant velocity.
 19. The method of claim 18, wherein the foam core of at least one of the balls has a density substantially different than the foam core of at least one other of the balls, such that the balls travel through air at different speeds despite being released at the substantially constant velocity.
 20. The method of claim 19, wherein the difference between the density of the foam core of the at least one of the balls and the density of the foam core of the at least one other of the balls is such that the balls travel through the air at speeds differing by at least about 10%.
 21. The method of claim 20, wherein the difference in density is such that the balls travel through the air at speeds differing by at least about 5% to about 20%.
 22. The method of claim 18, wherein: a diameter of the foam core of at least one of the balls is less than a diameter of the internal volume thereof such that a layer of air is located between an outside surface of the foam core and an inside surface of the hard shell; and a volume of the layer of air is such that the at least one of the balls and at least one other of the balls travel through air at different speeds despite being released at the substantially constant velocity.
 23. The method of claim 22, wherein the volume of air within the at least one of the balls is such that the balls travel through the air at speeds differing by at least about 10%.
 24. The method of claim 22, wherein the volume of air within the at least one of the balls is such that the balls travel through the air at speeds differing by at least about 5% to about 20%.
 25. The method of claim 18, wherein a plurality of the balls have substantially equal size.
 26. The method of claim 18, wherein a deviation of the size is one of: no greater than about 5%, no greater than about 2%, and no greater than about 1%.
 27. The method of claim 18, wherein the step of propelling the balls at the substantially constant velocity is carried out manually.
 28. The method of claim 18, wherein the step of propelling the balls at the substantially constant velocity is carried out by an automated machine.
 29. A system, comprising: a plurality of balls, each ball comprising: (i) a hard shell defining an internal volume and including a plurality of apertures therethrough; and (ii) a foam core disposed within the internal volume, wherein the foam core of at least one of the plurality of balls is adapted to cause such ball to travel through air at a substantially different speed as compared to at least one other of the plurality of balls despite the balls being released at a substantially constant velocity.
 30. The system of claim 29, wherein at least one of: at least one of the plurality of balls includes a foam core that fills the internal volume thereof; and at least one of the plurality of balls includes at least one spacer disposed between the outside surface of the foam core thereof and the inside surface of the hard shell thereof, the at least one spacer being adapted to position the foam core within the internal volume.
 31. The system of claim 30, wherein the at least one spacer is adapted to connect the outside surface of the foam core to the inside surface of the hard shell.
 32. The system of claim 29, wherein at least some of the plurality of balls include respective foam cores having respective porosities and/or compositions that are predetermined to achieve different respective densities; and the difference in density among the foam cores of the at least some of the plurality of balls are such that the balls travel through air at substantially different speeds despite being released at a substantially constant velocity.
 33. The system of claim 32, wherein the foam cores of the at least some of the plurality of balls are such that the balls travel through the air at speeds differing by at least about 5% to about 20%.
 34. The system of claim 29, wherein: at least some of the plurality of balls include respective foam cores having diameters that are less than diameters of the internal volumes such that respective layers of air are located between outside surfaces of the foam cores and inside surfaces of the respective hard shells; and respective volumes of the layers of air of the at least some of the plurality of balls are such that the balls travel through air at different speeds despite being released at the substantially constant velocity.
 35. The system of claim 34, wherein the respective volumes of the layers of air within the at least some of the plurality of balls are such that the balls travel through the air at speeds differing by at least about 10%.
 36. The system of claim 29, wherein the plurality of balls have substantially equal size. 